/Engine/Source/Runtime/Experimental/Chaos/Public/Chaos/Math/Poisson.h
Solve Poisson on a Uniform Grid (with standard 9-point Laplacian). Weights is a flattened array (using same indexing as UniformGrid and ArrayND) and the output solution. InConstrainedNodes is a list of flattened index nodes that are boundary conditions. ConstrainedWeights is a parallel array of the constrained values.
namespace Chaos { template<class TV, class T, bool NodalValues> void Chaos::PoissonSolve ( const [TArray](API\Runtime\Core\Containers\TArray)< int32 > & InConstrainedNodes, const [TArray](API\Runtime\Core\Containers\TArray)< TV > & ConstrainedWeights, const [TUniformGrid](API\Runtime\Chaos\Chaos\TUniformGrid)< T, 3 > & UniformGrid, const int32 MaxItCG, const TV CGTol, [TArray](API\Runtime\Core\Containers\TArray)< TV > & Weights, bool bCheckResidual, int32 MinParallelBatchSize ) }